Over the course of a year, taking cranberry capsules did nothing to stave off urinary tract infections (UTIs) among older women living in nursing homes, a US study has found.
There was no significant difference in the presence of bacteriuria plus pyuria in those who took cranberry capsules and those who took placebo capsules, the researchers found.
"I think it reinforces what many of the other studies have said so far," said lead author Dr. Manisha Juthani-Mehta, of the Yale School of Medicine in New Haven, Connecticut.
Previous studies on the use of cranberry products like juice and capsules produced mixed results. A systematic look at that evidence published in 2012 by the Cochrane Collaboration, an international organisation that evaluates and reviews medical research, concluded "cranberry juice cannot currently be recommended for the prevention of UTIs."
Originally, it was thought that eating or drinking cranberry products increased the acidity of urine and prevented UTIs. There was also speculation that proanthocyanidin in cranberries prevented bacteria from adhering to the bladder wall.
For the new study, the researchers randomly assigned 185 women over 65 years old living in 21 nursing homes near Yale to take daily either two capsules containing cranberry extracts including a total of 72 mg of proanthocyanidin, the equivalent of a person drinking a 20-ounce bottle of cranberry juice, or placebo capsules.
The researchers had a year of data on 147 women. Overall, there was no difference between women who took cranberry pills or placebos in the proportion who had bacteria and white blood cells in their urine at the end of the study period. Additionally, there was no difference between the two groups in the share of women who experienced symptomatic UTIs, died, were sent to hospitals or used antibiotics.
The results were published online October 27 in JAMA to coincide with presentation at Infectious Disease Week, which is being held in New Orleans.
"It is time to move on from cranberries," writes Dr. Lindsay Nicolle in an editorial accompanying the new study.
"The continuing promotion of cranberry use to prevent recurrent UTI in the popular press or online advice seems inconsistent with the reality of repeated negative studies or positive studies compromised by methodological shortcomings," writes Nicolle, of the University of Manitoba in Winnipeg, Canada.
Juthani-Mehta told Reuters Health that there is probably little downside to people eating or drinking cranberry products if they like, but she wouldn't recommend those as a way to prevent UTIs - especially among older adults who may be on a fixed income.
"Capsules can range from not a lot of money to $200 per month for a 30-day supply," she said.
For UTI prevention, Juthani-Mehta said there are a couple approaches people - especially women - can take, including making sure they stay hydrated.
"In terms of prevention, hydration is certainly important," she said. "The other factor in post-menopausal women is topical estrogen therapy among women who had recurrent UTIs. It has shown some benefit."
"We may not have a study to say drinking water can prevent UTIs, but that's really what I recommend," she said.